Aircraft nacelles are intended to house a turbojet engine, which can be a two-flow jet engine capable of generating a hot air flow (also called primary flow) from the combustion chamber of the turbojet engine, and a cold air flow (secondary flow) from the fan that circulates outside the turbojet engine through an annular channel, also called “stream,” formed between a fairing of the turbojet engine and an inner wall of the nacelle. The exhaust section of the secondary flow is called “secondary nozzle” while the exhaust of the primary flow is done in the primary nozzle. At the rear of the nacelle, the two primary and secondary flows mix.
This nacelle can be smooth or can be equipped with a thrust reverser device that, during landing, makes it possible to improve its braking capacity by reorienting at least part of the thrust generated by the turbojet engine towards the front. In this phase, the reverser obstructs the gas jet nozzle and orients the exhaust flow from the engine towards the front of the nacelle, thereby generating a counter-thrust that is added to the braking of the airplane's wheels.
In this perspective, the thrust reverser comprises a varied thrust reverser means, such as in general at least one mobile cowl, called “thrust reverser cowl,” moving in translation owing to actuators in a direction substantially parallel to a longitudinal axis of the nacelle. Thus, the mobile cowl(s) can alternatively go from a closing position in which the thrust reverser cowl(s) ensure(s) the aerodynamic continuity of the nacelle, to an open position in which a passage is revealed on a stationary structure of the nacelle to reverse the secondary flow.
Moreover, the nacelle can comprise an additional device allowing a variation of the exhaust section of the secondary nozzle. Such a device is commonly designated as a variable nozzle and can be associated with a thrust reverser device or can be incorporated into a smooth nacelle.
Although several variable nozzle embodiments exist, it is known to use, as device, a multitude of nozzle flaps able to pivot inside the stream so as to vary the width thereof. In this way it is possible to adapt the exhaust section of the second nozzle, so as to optimize the specific consumption of the turbojet engine or reduce the ejection noise of the gases depending on the flight phases.
One particular example is the embodiment described in French patent application 08/04295, where the nozzle flaps are situated at the output of the stream and also serve to produce a secondary nozzle variation during a limited translation of the thrust reverser cowl(s).
The nozzle flaps and the thrust reverser cowls constitute mobile panels. The movement of such panels is ensured by a plurality of actuators.
The actuators can assume different forms, in particular electromechanical actuators like those described in document EP 0 843 089.
This type of actuator is associated with an actuator system comprising at least one motor able to drive said actuators. The actuator system is intended in particular to mechanically actuate the actuators.
The availability of the thrust reverser and secondary nozzle section varying systems is an important consideration and constitutes one major area of development for electromechanical actuators.
The availability criterion refers to the capacity for the mobile panels of the thrust reverser and/or variable nozzle device to be deployed so as to fulfill their function and prevent operation in deteriorated mode. It requires an average redundancy level, without, however, severely damaging the reliability of the entire device, and an appropriate architecture to minimize the common modes such as mechanical blocking.